Generally, mass spectrometers measure mass-to-charge ratios of ions obtained from analyte samples, enabling identification of the molecular contents of the samples. Mass spectrometers include an ion source for ionizing the samples for subsequent fragmentation, analysis and detection. Different types of inlet devices provide the samples to the ion source for ionization. For example, in a liquid chromatograph mass spectrometer (LCMS), the inlet device is a liquid chromatograph device which provides molecular samples in liquid form, and in a gas chromatograph mass spectrometer (GCMS), the inlet device is a gas chromatograph device which provides molecular samples in gaseous form. Both types of mass spectrometers provide samples at atmospheric pressure. Mass spectrometers require these samples at vacuum pressures via a pressure reduction means.
To accomplish this task, one type of LCMS includes a capillary that is about 18 cm in length and has a central capillary bore of about 0.6 mm in diameter. In an LCMS, for example, the capillary receives ions from a vaporized sample of an effluent stream (e.g., analyte ion vapor) from an ion source, such as an electrospray ionization (ESI) ion source, and transports the received ions through the single capillary bore to an LCMS inlet region. However, the flow rate of ions through the single capillary bore is restricted, in part, by the physical dimensions of the capillary bore.
For example, a capillary bore having small diameter would typically have a lower ion flow rate than a capillary bore having a larger diameter. However, simply increasing the diameter of the capillary bore does not always result in a higher ion flow rate. For example, with respect to a capillary about 18 cm in length, it has been determined that the extraction of ions formed in a sample plume from a liquid chromatograph device is limited by the onset of turbulence and attendant ion losses in the capillary bore when the internal diameter of the capillary bore is increased beyond 0.9 mm, resulting in an actual reduction in the ion flow rate.
Attempts to improve ion flow include providing multiple metal capillaries (e.g., stainless steel), as described, for example, in U.S. Pat. No. 6,803,565 (Smith et al.), issued Oct. 12, 2004. However, metal capillary tubes are electrically conductive. Therefore, the metal capillary tubes are limited with respect to various techniques for attracting ions having different charges, and especially for transporting ions through potential differences in the capillary tubes, such as applying a potential difference across opposite ends of the capillary tubes.